1. Field of the Invention
The present invention relates to a technique of reducing the phenomenon known as color bleeding in the formation of a color image on ordinary paper, and obtaining a water-resistant ink image. The present invention particularly relates to a liquid composition to be used in an image formation process which employs an ink-jet system, to an ink set comprising a combination of the liquid composition and ink, and to image forming methods and apparatus which use the liquid composition and the ink set.
2. Related Background Art
In an ink-jet recording method, recording is performed by ejecting ink droplets and adhering the droplets to a recording medium such as paper. Particularly, in an ink-jet recording method in which bubbles are generated by applying heat energy to an ink using an electrothermal converter as discharge energy supply means, and the bubbles are used to discharge ink droplets, a high density multi-orifice recording head can be readily manufactured and can record high-resolution and high-definition images at a high speed. Such ink jet recording methods have been disclosed in, for example, Japanese Patent Publication Nos. 61-59911, 61-59912 and 61-59914.
However, since the ink used in a conventional ink-jet recording method generally comprises water as the main component, and a water-soluble high-boiling point solvent such as glycol for preventing drying and clogging of the nozzle, the method has the drawbacks that sufficient fixing properties cannot be obtained when recording on ordinary paper using such an ink, and that a nonuniform image is produced, possibly due to nonuniform distribution of filler and sizing agent on the surface of recording sheet. Furthermore, in the case of color recording, when a plurality of color inks are successively superimposed before one of the color inks is fixed to the recording sheet, there is the problem that a satisfactory image cannot be obtained due to color bleeding or nonuniform mixing at the boundary between images having different colors (This phenomenon is referred to as "bleeding" hereinafter).
To enhance the fixing properties, therefore, Japanese Patent Laid-Open No. 55-65269 discloses a method of adding a compound for increasing penetrability, such as a surfactant, to an ink. Japanese Patent Laid-Open No. 55-66976 discloses a method of using an ink comprising a volatile solvent as a main component. However, although the method of adding a surfactant or the like to the ink increases the penetrability of the ink into the recording paper and improves the fixing properties of the ink and decreases bleeding to some extent, the method also causes the problem of decreasing the image density and chroma due to deep penetration of the ink's coloring material into the recording sheet. The method also causes lateral spreading of the ink and consequently causes the problem of deteriorating the edge sharpness or resolution. On the other hand, since the latter method of using an ink comprising a volatile solvent as a main component not only produces the same problems as the former method but also readily produces clogging of a recording head nozzle due to the evaporation of the solvent, it is undesirable.
Methods of adhering a liquid to a recording medium before ejection of the ink in order to improve image quality have been proposed for solving the aforementioned problems.
For example, Japanese Patent Laid-Open No. 63-299971 discloses a method of recording with ink containing an anionic dye after adhering a liquid containing an organic compound having at least two cationic groups per molecule to the recording medium. Japanese Patent Laid-Open No. 64-9279 discloses a method of recording with an ink containing an anionic dye after adhering an acid liquid containing succinic acid or the like to the recording medium. Further, Japanese Patent Laid-Open No. 64-63185 discloses a method of recording with an ink after applying a liquid which makes the dye insoluble.
However, since all of the above methods have been proposed for improving bleeding and water resistance of an image by depositing dyes themselves, these methods do not sufficiently prevent bleeding between different color inks. In addition, since the deposited dyes are liable to be distributed nonuniformly on the recording sheet, the formed image has poor coverage of the pulp fibers of the recording sheet, thereby reducing the uniformity of the image.